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        <h3 class="post-title"><span>踩坑正则表达式-匹配字符串中的整数和小数</span></h3>
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        Calos 发表于
        <time datetime="2019-05-25T16:00:00.000Z">2019-05-26</time>
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    <div class="post-content">
        <p>首先，明白几个边界匹配器字符的含义。</p>
<p><code>^</code>：整行字符串的开头位置</p>
<p><code>\A</code>：整段字符串的开头位置</p>
<p><code>$</code>：整行字符串的结尾位置</p>
<p><code>\z</code>：整段字符串的结尾位置</p>
<p>​        关于<code>\b</code>和<code>\B</code>，官方原版的解释中是A word boundary和A non-word boundary，没有详细的解释，反正我是没看明白，自己测试一下，匹配字符串：<code>6lo.ve</code>，正则表达式：<font color="##90EE90"><code>\B\D</code></font>。结果共三处，包括<code>l</code>、<code>o</code>、<code>v</code> 三个字母。</p>
<p>​        那么我们是不是可以认为<code>\B\D</code>表示：匹配一个任意非数字的字符，并且字符的前一位是字母或者数字，此时这个单词不是边界单词；<code>\b\D</code>表示：匹配一个任意非数字的字符，并且字符的前一位不是字母或者数字，此时是一个边界单词。</p>
<hr>
<p>再来说说数字的匹配，先来一个示例字符串：<br>    <font color="#1E90FF"><code>&quot;78.64java23.678love98py3.4.5c78c++144vv7vv12..12r45v.56v56.&quot;</code></font><br>最简单的正则表达式为：<font color="##90EE90"><code>[0-9]+(\.[0-9]+)?</code></font>，可以匹配绝大多数的结果，但是如果字符串中包括<font color="#8B008B"><code>3.4.5</code></font>、<font color="#8B2252"><code>12..12</code></font>、<font color="#FF7F00"><code>.56</code></font>、<font color="#A020F0"><code>78.</code></font>这种数字的，会被匹配出来<font color="#8B008B"><code>3.4</code>、<code>5</code></font>，<font color="#8B2252"><code>12</code>、<code>12</code></font>，<font color="#FF7F00"><code>56</code></font>，<font color="#A020F0"><code>78</code></font>。</p>
<p>​        那我们是不是能把这几个特殊的去除掉呢？后来又想到一种匹配规则：<font color="##90EE90"><code>[0-9]+\.{0,1}[0-9]+\.{0}[0-9]</code></font>，你有没有发现这个匹配是有点问题的，你来看啊：</p>
<ul>
<li>第一个<code>.</code>前面的数字是一个或者多个，后面的数字也是一个或者多个；</li>
<li>第二个<code>.</code>后面的数字是一位，也就是说。</li>
</ul>
<p>也就是说，这个规则匹配到的<strong>数字至少是三位整数，如果带有小数的话，至少要带有两位小数（整数位至少也要保证一个位数）</strong></p>
<hr>
<p>假设字符串里面除了<strong>字母、数字和小数点</strong>不再包含别的东西，那么我们是不是可以试试另外一种匹配模式：<font color="##90EE90"><code>\B[0-9]+\.{0,1}[0-9]+\B</code></font>，这个匹配中<code>\B</code>表示数字旁边的必定是一个单词（即数字或者字母），这样就可以排除掉<code>3.4.5</code>、<code>12..12</code>、<code>.56</code>、<code>56.</code>这种类型的数字，但是这个也有一些缺点：</p>
<ul>
<li>字符串只包含字母、数字和小数点；</li>
<li>匹配的数字是从两位起步的；</li>
<li>字符串的开头和结尾不能为数字，不然会被舍弃掉，例如上述字符串中<code>78.64</code>会变成<code>8.64</code>，这个问题可以通过在字符串两边各加一个字母解决掉。</li>
</ul>
<hr>
<p>暂时爬坑到这里，后续有进展接着更新…</p>

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